Figure 6-19 RIVUXG Seasons on the Martian Surface (a) This view from Viking Lander 1 shows rocks that resemble volcanic rocks on Earth (see Figure 5-2a). They are thought to be part of an ancient lava flow that was broken apart by crater-forming asteroid impacts. Fine-grained debris has formed sand dunes. (b) This picture was taken during midwinter at the Viking Lander 2 site. Freezing carbon dioxide adheres to water ice crystalsand dust grains in the atmosphere, causing them to fall to the ground and coat the surface with frost. This frost lasted for about 100 days.